The goal of this project is to identify genes that are involved in susceptibility and resistance to human vaccinia infection, and, consequently, in some of the adverse effects seen with smallpox vaccination. We (R.B.B.) recently led a multi-center prospective study on the clinical response to vaccinia immunization in 680 naive individuals. Among the 665 individuals responding to the vaccine, 84 (13%) developed fever, muscle aches and lymphadenopathy giving rise to what we have called Acute Vaccinia Syndrome (AVS) in approximately 30% of vaccines. The timing of the onset of these symptoms matched the timing of the highest levels of viral shedding, indicating that fever, and the other components of AVS appear to be secondary to the virus. We hypothesize that individuals developing AVS (and especially fever) have disease-predisposing alleles that are associated with abnormal innate immune or delayed adaptive immune responses to vaccinia. These individuals may be more susceptible to poxviruses in general, and could constitute a group at increased risk for mortality if exposed to smallpox. We propose to identify genes that are expressed in response to vaccinia infection at the site of inoculation and systemically using a transcriptional analysis. We will compare responses between individuals that develop AVS, and those individuals who develop no adverse reactions to immunization. These studies will provide us with a transcriptional profile of the host response to vaccinia infection, identify key molecules in the host response, and, establish parameters for protective immune responses that could be used to test the efficacy of new vaccines. We will also identify alleles associated with adverse effects to vaccinia immunization and abnormal innate immune responses to the virus through the analysis of haplotypes based on single nucleotide polymorphisms in candidate genes. The identify of these alleles may provide clues to the critical elements of the host response to poxvirus, and could provide a method to identify individuals at increased risk for adverse effects to the vaccine, or more severe disease with poxvirus infection. The design of the study, with the inclusion of transcriptional profiling of individuals receiving vaccinia immunization coupled with a detailed virologic and immunologic profile, ensures that we will obtain valuable information on the host response to vaccinia immunization.